F5 stock showed a nearly 146 percent increase last year, No. 1 on the list. It was also among the top 10 companies in profit margin, market capitalization and return on assets.

Buy an airline ticket, rent a movie, do some day trading, download a video game, get cash from an ATM or purchase an item online and the chances are you’re running fast and safe, thanks to the hardware and software of F5 Networks.

You’ll never know it. F5 serves the companies that serve consumers. As Chief Executive John McAdam said, “The beauty is, we sit between the application running on a computer and the Net.” F5 makes sure its clients’ servers run at maximum efficiency, and that data are secure.

Investors do know, and they’re happy. The Seattle company turns in some of the strongest performance numbers in this year’s Best of the Northwest. F5 stock showed a nearly 146 percent increase last year, No. 1 on the list. It was also among the top 10 companies in profit margin, market capitalization and return on assets. The company has no debt.

Tour F5’s headquarters overlooking Elliott Bay, and you’ll find the technology center, where the company shows off its products to potential clients. White noise indicates the cooling needed to keep the servers in good order. Hanging overhead are flags of some of the company’s customers: Microsoft, SAP, Dell, Oracle and Hewlett-Packard among them.

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In fact, F5’s customers include 43 of the Fortune 50 and 60 percent of the Fortune 500. The 15 top commercial banks, six largest airlines, 10 biggest insurance companies and 14 out of 15 executive departments in the federal government depend on F5 technology. So do 17 out of 20 cloud infrastructure and Web-hosting outfits. Microsoft and Apple may hate each other, but both use F5. Customers span the globe.

McAdam, a Scotsman with a rich brogue and a shy smile, became CEO in 2000, just in time to navigate the dot-com bust. When the Great Recession hit, F5 was ready. Although it saw a slowdown in December 2008, by March business was picking up again.

“I spend a lot of my time working with Wall Street,” he said. That means scrutinizing the financials on a “granular” level, with daily revenue reports and the ability to make decisions on a weekly basis. “But the real key is, we drive our business. If we do that well, we will be liked.”

Still, staying on top means F5 must keep up with the new information-technology infrastructure being deployed by its customers, and changing consumer appetites and demands. “It’s a time of massive change,” McAdam said.

But that’s where F5 thrives — even if most users in the cloud never know it’s there.

You may reach Jon Talton at jtalton@seattletimes.com